Strengthening of constructional steels using TMT methods including deformation in the intercritical temperature range

Conclusions

• 1. Steel 15G2SF treated by a TMT method consisting of preliminary austenitization at temperatures above$A_{C_3 }$, followed by cooling to the temperature of the middle of the intercritical temperature range, than by 50% deformation, and by water cooling and high-temperature tempering at 620–650°C, acquires high tensile strength (σ_y ≥ 600 MPa, σ_u ≥ 700 MPa) and ductility, together with unusually high impact toughness at subzero temperatures (a ⁻⁷⁰_0.25 ≥2.0 MJ/m²,a ⁻⁷⁰_t ≥1.0 MJ/m².

• 2. The treatment studied has some economic and technological advantages in comparison with controlled rolling at temperatures below$A_{r_3 }$. For instance, the optimum results can be achieved using cheap, Nb-free steel 15G2SF. The high-temperature tempering makes precise control of the treatment in the intercritical temperature range unnecessary.